Hidden in attic over time (6)
I believe the answer is:
covert
'hidden' is the definition.
(similar in meaning)
'in attic over time' is the wordplay.
'in' indicates a hidden word.
'COVERT' is hidden in the letters of 'attic over time'.
(Other definitions for covert that I've seen before include "Hidden, secret" , "Undercover, secret" , "Area of undergrowth in which animals hide" , "Not openly displayed" , "place for game" .)